1. Winter Processes in WEPS Fred Fox Wind Erosion Research Unit Manhattan, KS

2. Wind Erosion Essentials ● Dry Aggregate Stability ● Aggregate Size Distribution ● Surface Soil Water Content  Suppression affect decreases below wilting point ● Snow Cover ● Vary in Time ● Affected by Intrinsic Soil Properties ● Climate Driven ● Diurnal Factors

3. Aggregate Stability Processes ● Wetting (frozen or warm) ● Drying (frozen or warm) ● Freezing ● Thawing  Puddling  Shrink ● Freeze / Thaw (same day)

4. Temperature Model ● Layers  Snow  Residue (thermal conductivity only)  Soil (same as hydrology layers)

5. Temperature Model ● Daily Energy Balance  Net Radiation on Surface (Horizontal, Albedo Adjusted Short Wave, Atmosphere Adjusted Long Wave)  Thermal Conductivity (Soil State and Property)  Heat Capacity (Soil State and Property) ● Diurnal Variation  Attenuation of Diurnal Air Temperature Wave

6. Snow State ● Temperature ● Depth ● Water Content ● Fraction of Snow Water Which is Frozen

7. Soil Thermal State ● Temperature ● Water Content ● Fraction of Soil Water Which is Frozen ● Bulk Density

8. Surface Water Content Processes ● Soil Surface Evaporation  Snow cover  Canopy (living and dead)  Residue (standing and flat)  Soil State  Soil Properties ● Upward Soil Water Movement  Soil State  Soil Properties

9. Soil State ● Bulk Density ● Hydraulic Conductivity ● Soil Water Release Curve (hysteresis?) ● Water Content

10. Daily Calculation ● Water inflow  Precipitation (snow or rain based on air temperature)  Irrigation (always liquid, at air temperature)  Gives new snow depth, water content, temperature, fraction water frozen ● Energy Balance  New energy content, density, water for infiltration